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Atherosclerosis (AS) is the single most common cause of heart disease and is the major contributor to the development of angina, heart attacks and stroke. Despite the introduction of statin-based therapy to reduce levels of plasma low density lipoprotein (LDL) cholesterol, the epidemic of heart disease is claiming tens of thousands of lives each year, particularly in Western countries and costs the health system over billions of dollars per year (National Health Survey: Summary of Results, Australia, 2004-05, cat. no. 4364.0, ABS, Can berra, Vol: Australian Bureau of Statistics, 2006, (AIHW) AIoHaW. Health system expenditure on disease and injury in Australia, 2000-01. Health and Welfare Expenditure Series No. 19, 2004; HWE 26).
Atherosclerosis begins to develop early in life and progresses with time. However, the rate of progression is, to a large extent, unpredictable and differs markedly amongst seemingly comparable individuals. One of the early events leading to Atherosclerosis is the formation of “fatty streaks”, deposits of monocytes, macrophages, foam cells and lipids within the intima of the arterial wall. Fatty streaks exist in most adults and can remain as fatty streaks for years or decades, having little or no adverse clinical effects. Some, but not all, fatty steaks progress into fibriolipid plaques which are distinguished by the presence of smooth muscle cells and increased extracellular fibres within the intima. Cell death within the plaque leads to the formation of a necrotic core, the accumulation of extracellular material and the formation of the complex plaque. At this stage, the plaque may severely restrict blood flow leading to a range of clinical complications; however, many individuals will be unaware of the problem and show no symptoms.
Complex plaques can become unstable (a “vulnerable” plaque) as a result of the thinning of the smooth muscle cell layer over the plaque. Unstable plaques may rupture leading to thrombosis, myocardial infarction and stroke with the associated morbidity and mortality (the “vulnerable” patient). Although plaque accumulation and development is progressive throughout life, the switch from stable to unstable plaque can occur earlier or later in the disease process. Thus a 45 year old with relatively low levels of plaque can become unstable leading to a coronary event.
Despite our detailed knowledge of plaque pathology and progression many individuals have no clinical symptoms and so are unaware of their risk. In 30 to 50% of these individuals, the first indicator of Atherosclerosis is an acute heart attack which is often fatal (Heart Disease and Stroke Statistics-2006 Update, Dallas Tex.: American Heart Association, 2006. Available at http://www.americanheart.org/downloadable/heart/1198257493273HS_Stats%202008.pdf)
A non-invasive assay is required to identify and monitor heart disease.